1. Field of the Invention
The present invention relates to optical fiber communication systems. More particularly, the present invention relates to bi-directional telemetry and service channels for use with optical fiber communication systems.
2. Related Art
Optical fibers can be used to carry signals over great distances. As such, optical fibers are advantageous for use in a communication system to carry communication signals representing, for example, customer voice, data, or video (referred to herein as "customer traffic" or "commercial traffic"). Such an optical fiber communication system also advantageously provides some mechanism for the transmission of service communications. Service communications can include, for example, telemetry signals that provide control or command signals, or status signals, for equipment located within the optical fiber communication system. Service communications can also include service signals representing voice communication between maintenance personnel located at various sites within the optical fiber communication system.
One conventional method for providing telemetry signals (e.g., alarms, temperature conditions, equipment failure, etc.) is through the use of a Synchronous Optical Network (SONET). The SONET data structure is split into a "payload" area that carries customer traffic, and an "overhead" area that includes dedicated bits for communication between network elements. The SONET overhead area enables communication for Operations, Administration and Maintenance (OA&M) between parts of the network via the transmission path carrying customer traffic, rather than needing physically separate signaling networks. The telemetry information is available once the optical signals are converted into electronic signals. Such conversion is done to recover and clean up the signals. However, the amount of information that can be sent via the overhead area is fixed by the number of dedicated bits.
Alternatively, telemetry signals can be provided in optical form by using wavelengths outside of the wavelength window used for carrying customer traffic. For example, conventional equipment available from Pirelli Cavi S.p.A., Milan, Italy uses wavelengths in the range from 1200 to 1400 nm (nanometers) to carry service signals, and wavelengths in the range from 1500 to 1600 to carry customer traffic. Such conventional equipment is described in U.S. Pat. No. 5,113,459, the entirety of which is incorporated herein by reference. Such conventional equipment provides for the transmission of telemetry signals at the selected wavelength (for example, 1310 nm) in one direction on one fiber. In order to transmit telemetry signals in the opposite direction using such conventional equipment, a second fiber is needed. Therefore, two fibers are required to provide for bi-directional transmission of telemetry signals.
Two fibers can be used to provide redundancy in an optical fiber communication system. One fiber can be used as the primary or "working" fiber, and the second fiber can be used as the secondary or "protection" fiber. Because two fibers are required to provide for bi-directional transmission of telemetry signals, two fibers cannot provide redundancy for bi-directional transmission of telemetry service signals. Rather, more than two fibers are conventionally required to provide a "protected" bi-directional telemetry signal. If the working fiber fails and communication is switched to the protection fiber in a conventional system, then bi-directional transmission of telemetry signals is lost. In such a scenario, telemetry signals could only be uni-directionally transmitted in the single direction provided by the protection fiber.
Thus, there is a need in the art for a system and method that provides for the bi-directional transmission of telemetry signals using a single fiber. There is a further need in the art for a system and method that provides for a fully-protected bi-directional telemetry service channel using only two fibers.